Many systems exist for the detection of flaws in a moving web of material wherein the web is illuminated by a scanning light beam which moves rapidly across the width of the web, combined with a light collecting device and a photocell to sense modulation by the web of light either transmitted or reflected to the photocell. In most cases the photocell output is fed to an elaborate computer designed to identify the size and nature of the flaw detected based on signal characteristics. Most systems fail to recognize the nature of the flaw because the light collecting system does not provide readily distinguishable differences in signal on which the electronic circuitry must operate.
For example, U.S. Pat. No. 3,700,909 in the name of Murray, et al., and of common assignment with the instant invention, employs a photomultiplier tube which receives all of the light which passes through variously sized pinhole defects in a web of opaque material. As taught in this prior patent, the entire amount of light passing through the pinhole is allowed to impinge upon the photomultiplier, thereby determining the amplitude of the photomultipliers signal. Similarly, our prior U.S. Pat. No. 3,755,674, also in the name of Murray, et al., processes a signal generated in response to the amount of light passing through a pinhole defect in an opaque material.
U.S. Pat. No. 3,588,513, in the name of Akamatsu, et al., additionally illustrates a photoelectric inspection system wherein the light reflected, or intercepted, by surface defects on a moving web may be used to generate a variable voltage signal.
U.S. Pat. No. 3,448,279, in the name of Lindemann, et al., represents another type of photoelectric inspection system wherein inspection of a web, such as cloth, is effected by simple light collections, through various transmittance and reflectance sensors, with any subsequent flaw classification requiring involved electronic signal processing equipment.